Without limiting the scope of the invention, its background is described in connection with optical polarizers/isolators. It is widely believed that the complete integration of electronics and photonics on a submicron scale [1] must be accomplished in the near future. Thus the toolbox of integrated photonics is rapidly expanding, reflecting recent technological advances in photonic crystals [2], dielectric waveguides [3], and magnetooptic materials [4]. Optical polarizers (devices that transmit only one light polarization) and related to them isolators (one-way optical elements that suppress reflection of at least one polarization) are particularly challenging to make in the integrated form.
Chiral twisted fiber gratings with a “perfect” double-helical perturbation of the refractive index have been suggested as polarization selective filters in the optical [6] and microwave [7, 8] frequency range. But, twisting is incompatible with silicon-based waveguides, which are also difficult to fabricate with cross sections different from the rectangular one. Accordingly, there is a need for an apparatus and method for a waveguide-based optical polarizer/isolator.